Control of heart rate

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How does the heart beat:
The heart muscle is myogenic, it can contract without external nervous stimulation. Contraction of the cardiac muscle is initiated by small changes in the electrical charge of cardiac muscle cells , when these cells have a slight positive charge on the outside they are polarised. when this charge is reversed they are depolarised, a change in polarity spreads like a wave from cell to cell causing the cells to contract.

Depolarisation starts in the sinoatrial node which is located in the wall of the right atrium, beneath the opening to the superior vena cava, the SAN (sinoatrial node) is also called the pacemaker.

  • Electrical impulses from the SAN spread across the atria walls, causing contraction.
  • impulses pass to the ventricles via the atrioventricular node (AVN).
  • impulses pass down the purkyne fibres to the heart


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